Atomic layer deposition of GeO2

ABSTRACT

Atomic layer deposition processes for forming germanium oxide thin films are provided. In some embodiments the ALD processes can include the following: contacting the substrate with a vapor phase tetravalent Ge precursor such that at most a molecular monolayer of the Ge precursor is formed on the substrate surface; removing excess Ge precursor and reaction by products, if any; contacting the substrate with a vapor phase oxygen precursor that reacts with the Ge precursor on the substrate surface; removing excess oxygen precursor and any gaseous by-products, and repeating the contacting and removing steps until a germanium oxide thin film of the desired thickness has been formed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 14/867,833, filed Sep. 28, 2015, which is a continuation of U.S. patent application Ser. No. 13/802,393, filed Mar. 13, 2013, now U.S. Pat. No. 9,171,715, which claims priority to U.S. Provisional Application No. 61/697,007, filed Sep. 5, 2012, and U.S. Provisional Application No. 61/713,082, filed Oct. 12, 2012, each of which is incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The application relates to atomic layer deposition processes for forming GeO₂ films.

Background

Ge devices are of interest because of Ge high hole mobility. Low D_(a) interface formation with HfO₂ HK material will allow for good Ge based FinFETs.

SUMMARY

According to some embodiments of the present disclosure, atomic layer deposition processes for forming germanium oxide thin films on a substrate in a reaction chamber are disclosed. The ALD processes can include contacting the substrate with a vapor phase tetravalent Ge precursor, removing excess Ge precursor and any reaction by-products, contacting the substrate with a vapor phase oxygen precursor, removing excess oxygen precursor and any gaseous by-products, and repeating the contacting and removing steps until a germanium oxide thin film of the desired thickness has been formed. In some embodiments, contacting the substrate with a vapor phase tetravalent Ge precursor results in the formation of at most a molecular monolayer of the Ge precursor on the substrate surface. In some embodiments, the oxygen precursor reacts with the Ge precursor on the substrate surface.

According to some embodiments of the present disclosure, in an ALD process for forming a germanium oxide thin film using a Ge precursor and an oxygen precursor, removing excess Ge precursor comprising removing excess Ge precursor from the substrate surface and in the proximity of the substrate surface. In some embodiments, the oxygen precursor is something other than water. In some embodiments, the oxygen precursor is one of ozone, oxygen atoms, oxygen radicals, or oxygen plasma. In some embodiments, the Ge-precursor is not a halide. In some embodiments, the Ge-precursor comprises at least one alkoxide ligand. In some embodiments, the Ge-precursor comprises at least one amine or alkylamine ligand. In some embodiments, the Ge-precursor comprises at least one amine or alkylamine ligand, and the oxygen precursor comprises water.

According to some embodiments of the present disclosure, in an ALD process for forming a germanium oxide thin film on a substrate, the surface of the substrate comprises a thin layer of GeO₂ prior to beginning the ALD process. In some embodiments, the substrate is pretreated with a passivation chemical to prevent oxidation before the germanium oxide film is deposited. In some embodiments, an interfacial layer is formed on the substrate before the germanium oxide thin film is deposited. In some embodiments, the deposition temperature is from about 100° C. to about 400° C. In some embodiments, the substrate is treated to remove native Ge oxide prior to forming the germanium oxide thin film.

Some embodiments for forming a germanium oxide thin film by an ALD process include depositing a thin layer of a different material over the germanium oxide thin film. In some embodiments, the thin layer of a different material is deposited directly on the germanium oxide thin film. In some embodiments, the thin layer comprises Al₂O₃, and in some embodiments, the Al₂O₃ layer is deposited by a process that does not use water as a reactant. In some embodiments, the germanium oxide thin film serves as an interlayer between the substrate and a high-k layer. And in some embodiments, the germanium oxide thin film may be used in a Ge-condensation process.

According to some embodiments, an atomic layer deposition process is disclosed for forming a pure GeO₂ thin film, in which the process can include alternately and sequentially contacting a substrate with Ge(OCH₂CH₃)₄ and O₃.

According to some embodiments, an atomic layer deposition process is disclosed for forming a pure GeO₂ thin film, which can include alternately and sequentially contacting a substrate with an alkylamine Ge precursor and an oxygen source. In some embodiments, the Ge precursor is TDMAGe, and the oxygen source is ozone. And in some embodiments, the Ge precursor is TDMAGe, and the oxygen source is water. In some embodiments, the oxygen source is water.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Description and from the appended drawings, which are meant to illustrate and not to limit the invention, and wherein:

FIG. 1 illustrates the growth rate of GeO₂ films as a function of deposition temperature using vapour pulses of Ge(OEt)₄ and O₃ at 150° C.-300° C.;

FIG. 2 illustrates two computerized images of the respective thicknesses of two wafers prepared according to some embodiments.

FIG. 3 illustrates GeO₂ film thickness non-uniformity as a function of deposition temperature using vapour pulses of Ge(OEt)₄ and O₃ at 150° C.-300° C.;

FIG. 4 illustrates GeO₂ film thickness as a function of the number of deposition cycles when using vapour pulses of Ge(OEt)₄ and O₃ at 250° C.;

FIG. 5 shows the composition of GeO₂ deposited by ALD at various temperatures.

FIG. 6A shows GeO₂ films deposited by ALD over Ge at a first magnification. HfO₂ was subsequently deposited over the GeO₂;

FIG. 6B shows GeO₂ films deposited by ALD over Ge at a second magnification. HfO₂ was subsequently deposited over the GeO₂;

FIG. 7A illustrates GeO₂ film thickness as a function of the number of deposition cycles when using vapour pulses of Ge(OEt)₄ and O₃ at 300° C. on HF-last Si;

FIG. 7B illustrates GeO₂ film thickness as a function of the number of deposition cycles when using vapour pulses of Ge(OEt)₄ and O₃ at 300° C. on HF-last Ge;

FIG. 8A shows a transmission electron microscope (TEM) image of two layers deposited by ALD (GeO₂ and Al₂O₃) where the Al₂O₃ was deposited using a TMA+O₃-process.

FIG. 8B shows a TEM image of three intermixed layers (Al, Ge, and O) when Al₂O₃ was deposited using a TMA+H₂O process.

FIG. 9A shows an image from a scanning electron microscope (SEM) at a first magnification illustrating GeO₂ film conformality when deposited using vapour pulses of Ge(OEt)₄ and O₃.

FIG. 9B shows an image from a SEM at a second magnification illustrating GeO₂ film conformality when deposited using vapour pulses of Ge(OEt)₄ and O₃.

FIG. 10 illustrates ALD GeO₂/ALD HfO₂ stack film conformality when grown at reaction temperature of 250° C. The target thickness of the GeO₂ was about 30 nm.

FIG. 11 illustrates the C-V characteristics of ALD GeO₂ interlayers grown on p-doped Ge and n-doped Ge. The GeO₂ interlayers were grown at a reaction temperature 250° C. from vapour pulses of Ge(OEt)₄ and O₃.

FIG. 12 illustrates the C-V characteristics of GeO₂ interlayer grown by ALD at different temperatures using vapour pulses of Ge(OEt)₄ and O₃.

FIG. 13A illustrates the C-V characteristics of GeO₂ interlayers, grown by ALD at a reaction temperature of 250° C. using vapour pulses of Ge(OEt)₄ and O₃ with an ALD Al₂O₃ capping layer.

FIG. 13B illustrates the C-V characteristics of GeO₂ interlayers, grown by ALD at a reaction temperature of 250° C. using vapour pulses of Ge(OEt)₄ and O₃ without an ALD Al₂O₃ capping layer.

FIG. 14A illustrates the C-V characteristics of GeO₂ interlayers grown by ALD on Ge-substrates with HF-cleaning, at a reaction temperature 250° C. using vapour pulses of Ge(OEt)₄ and O₃.

FIG. 14B illustrates the C-V characteristics of GeO₂ interlayers grown by ALD on Ge-substrates without HF-cleaning, at a reaction temperature 250° C. using vapour pulses of Ge(OEt)₄ and O₃.

DETAILED DESCRIPTION

In one aspect, methods of depositing GeO₂ thin films by atomic layer deposition are provided. In some embodiments a GeO₂ thin film is formed on a substrate by a vapor deposition process comprising alternately and sequentially contacting a substrate with a vapor phase germanium precursor and an oxygen reactant, such that a layer of the germanium precursor forms on the substrate surface, and the oxygen-containing reactant subsequently reacts with the germanium precursor to form a GeO₂ thin film.

In some embodiments the Ge precursor may be selected from Germanium ethoxide (GeOEt)₄ and tetrakis(dimethylamino) germanium (TDMAGe). Other possible germanium precursors are provided below. In some embodiments the Ge precursor is not a halide. In some embodiments, the Ge precursor contains halide in at least one ligand, but not in all ligands.

In some embodiments the oxygen reactant comprises one or more of ozone, oxygen atoms, oxygen radicals, and oxygen plasma. In some embodiments the oxygen reactant may be water. However, in other embodiments the oxygen reactant is not water.

In some embodiments, GeO₂ thin films are deposited by alternately and sequentially contacting a substrate with Ge(OCH₂CH₃)₄ and O₃. In some embodiments GeO₂ thin films are deposited by alternately and sequentially contacting a substrate with tetrakis(dimethylamio) germanium (TDMAGe) and O₃.

GeO₂ films may be used, for example as an interface layer between high-k and new channel materials in semiconductor devices. For example, the GeO₂ layer may serve as an interface in a Ge-based FinFET. In some embodiments the GeO₂ layer is an interface layer between Ge and a high-k material. The GeO₂ interface layer may prevent leakage and decrease trap density. Other contexts in which GeO₂ thin films may be utilized will be apparent to the skilled artisan. For example, GeO₂ thin films may find use in optical applications. In some embodiments, the GeO₂ films deposited by ALD processes are annealed after the deposition as desired depending on the application.

In one embodiment, the GeO₂ films deposited by ALD can be used for a process called Ge-condensation. A principle of this can be seen and understood, for example, from U.S. Patent Publications 2011/0147811 (see FIGS. 3a and 3b ) and 2011/0193178 (see para. [0020, which are incorporated by reference herein]). By adding a GeO₂ film to the interface of Si_(1-x)Ge_(x)SiO₂, it may be possible for more Ge to be driven to the fin or channel material. In these cases it is preferable to cap the ALD-deposited GeO₂ film with another film (i.e., a “capping layer”), preferably one deposited by ALD or PEALD, such as ALD-deposited or PEALD-deposited Al₂O₃, SiN_(x), or SiO₂ before an anneal step where Ge will be driven to the fin or channel. In this application of Ge-condensation, water may be used as an oxygen source in the ALD GeO₂ process. In some embodiments, the GeO₂ is deposited by an ALD process on a silicon fin without further depositing a capping layer. In some embodiments, the GeO₂ is deposited by an ALD process on a Si_(1-x)Ge_(x) fin without further depositing a capping layer. In some embodiments, the GeO₂ is deposited by an ALD process on a silicon fin and a capping layer is deposited over the GeO₂ layer. In some embodiments, the GeO₂ is deposited by an ALD process on a Si_(1-x)Ge_(x) fin, and a capping layer is then deposited over the GeO₂ layer. In some embodiments, the capping layer is SiO₂. In some embodiments, the capping layer is SiN_(x). In some embodiments, the capping layer is Al₂O₃. In some embodiments, the capping layer is deposited by methods other than an ALD or PEALD process. In some embodiments, the capping layer is deposited by an ALD process. In some embodiments the capping layer is deposited by a PEALD process.

In some embodiments the GeO₂ films deposited by ALD are pure GeO₂ films. Thus, deposited GeO₂ may be able to produce a better interface layer than GeO₂ formed by thermal oxidation.

Atomic layer deposition allows for conformal deposition of GeO₂ films. In some embodiments, the GeO₂ films deposited by ALD have at least 90%, 95% or higher conformality. In some embodiments the films are about 100% conformal.

The substrate may be, for example, a semiconductor substrate. In some embodiments the surface of the substrate comprises a group III or group IV compound. For example, in some embodiments the surface of the substrate comprises Ge. In some embodiments the surface of the substrate comprises a thin GeO₂ layer. The GeO₂ layer may be formed, for example, through thermal or plasma oxidation. In some embodiments the substrate surface is H-terminated. In some embodiments native Ge oxide is removed, for example with HF, prior to GeO₂ deposition by ALD.

The substrate may be treated prior to depositing the GeO₂ layer by ALD. For example, the substrate may be treated with a passivation chemical to prevent oxidation prior to depositing GeO₂ by ALD. In other embodiments the substrate is treated to form an interfacial layer prior to depositing GeO₂ by ALD. For example, the substrate treatment may comprise exposing the substrate to trimethylaluminum (TMA) to form an interfacial layer or surface termination on the surface prior to GeO₂ deposition. As mentioned above, in some embodiments the substrate may be treated to remove native Ge oxide, for example with HF, prior to depositing GeO₂ by ALD.

In some embodiments, following GeO₂ deposition, a further film is deposited. The additional film may be directly over and contacting the ALD-deposited GeO₂ layer. In some embodiments a high-k film is deposited after the ALD-deposited GeO₂ is deposited. The high-k layer or other film may be deposited by ALD or by other known deposition methods. In some embodiments a HfO₂ layer is deposited over the GeO₂ layer. In some embodiments an Al₂O₃ layer is deposited over the GeO₂ layer. Without being bound to any particular theory, it is believed that water in the deposition process of the layer deposited on top of a GeO₂ layer may cause in some situations the intermixing of the already deposited GeO₂ layer and the layer deposited on top of GeO₂ layer. In some embodiments this mixing is preferable. In other embodiments, this mixing is to be avoided. Thus, in some embodiments a deposition process for depositing a film on top of a GeO₂ film does not utilize water as one of the reactants. In some embodiments a deposition process for depositing a film on top of a GeO₂ film utilizes an oxygen source other than water. In some embodiments, a deposition process for a film deposited on top of a GeO₂ film uses ozone as an oxygen source. In some embodiments a deposition process for a film deposited on top of a GeO₂ film uses oxygen atoms, oxygen radicals or oxygen containing plasma as an oxygen source. In some embodiments, a deposition process for a film deposited on top of a GeO₂ film uses water, and at least one mixed layer comprising germanium is produced. When a Ge substrate is used and ozone or oxygen plasma are provided as an oxygen source, atoms or radicals may oxidize the substrate during the first one or more ALD cycles for forming GeO₂ and form a thin layer of GeO₂ on the substrate itself. In that situation, the GeO₂ layer would be a kind of composite of GeO₂ (oxidized from substrate) and ALD-deposited GeO₂.

In some embodiments a GeO₂ layer is an interlayer between a substrate and high-k layer. Preferably a GeO₂ interlayer has a thickness of less than about 10 nm, more preferably less than about 5 nm and most preferably less than about 3 nm. In some cases the GeO₂ interlayer is less than about 2 nm or even less than about 1 nm thick.

Atomic Layer Deposition (ALD)

As noted above, processes described herein enable use of atomic layer deposition techniques to deposit conformal GeO₂ layers. Among vapor deposition techniques, ALD has the advantage of providing high conformality at low temperatures.

ALD type processes are based on controlled, self-limiting surface reactions of precursor chemicals. Gas phase reactions are avoided by feeding the precursors alternately and sequentially into the reaction chamber. Vapor phase reactants are separated from each other in the reaction chamber, for example, by removing excess reactants and/or reactant by-products from the reaction chamber between reactant pulses.

Briefly, a substrate is loaded into a reaction chamber and is heated to a suitable deposition temperature, generally at lowered pressure. Deposition temperatures are maintained below the precursor thermal decomposition temperature but at a high enough level to avoid condensation of reactants and to provide the activation energy for the desired surface reactions. Of course, the appropriate temperature window for any given ALD reaction will depend upon the surface termination and reactant species involved. In some embodiments the deposition temperature is from about 20° C. to about 600° C., preferably from about to 100° C. to about 400° C., and more preferably from about 150° C. to about 300° C.

A first germanium reactant is conducted into the chamber in the form of vapor phase pulse and contacted with the surface of a substrate. In some embodiments the substrate surface comprises a three dimensional structure. Conditions are preferably selected such that no more than about one monolayer of the germanium precursor is adsorbed on the substrate surface in a self-limiting manner. Excess first reactant and reaction byproducts, if any, may be removed from the substrate and substrate surface and from proximity to the substrate and substrate surface. In some embodiments reactant and reaction byproducts, if any, may be removed by purging. Purging may be accomplished for example, with a pulse of inert gas such as nitrogen or argon.

Purging the reaction chamber means that vapor phase precursors and/or vapor phase byproducts are removed from the reaction chamber such as by evacuating the chamber with a vacuum pump and/or by replacing the gas inside the reactor with an inert gas such as argon or nitrogen. Typical purging times are from about 0.05 seconds to about 20 seconds, more preferably between about 1 second and about 10 seconds, and still more preferably between about 1 second and about 2 seconds. However, other purge times can be utilized if necessary, such as when depositing layers over extremely high aspect ratio structures or other structures with complex surface morphology. The appropriate pulsing times can be readily determined by the skilled artisan based on the particular circumstances.

Another method for removing excess reactants—metal precursors or oxygen precursors, reaction byproducts, etc.—from the substrate surface or from the area of the substrate may involve physically moving the substrate from a location containing the reactant and/or reaction byproducts.

A second gaseous oxygen reactant is pulsed into the chamber where it reacts with the first germanium reactant on the surface to form germanium oxide. Excess second reactant and gaseous by-products of the surface reaction are removed from the substrate, for example by purging them out of the reaction chamber, preferably with the aid of an inert gas. The steps of pulsing and removing are repeated until a thin film of the desired thickness has been formed on the substrate, with each cycle typically leaving no more than about a molecular monolayer.

As mentioned above, each pulse or phase of each cycle is preferably self-limiting. An excess of reactant precursors is supplied in each phase to saturate the susceptible structure surfaces. Surface saturation ensures reactant occupation of all available reactive sites (subject, for example, to physical size or “steric hindrance” restraints) and thus ensures excellent step coverage. In some arrangements, the degree of self-limiting behavior can be adjusted by, e.g., allowing some overlap of reactant pulses to trade off deposition speed (by allowing some CVD-type reactions) against conformality. Ideal ALD conditions with reactants well separated in time and space provide near perfect self-limiting behavior and thus maximum conformality, but steric hindrance results in less than one molecular layer per cycle. Limited CVD reactions mixed with the self-limiting ALD reactions can raise the deposition speed.

In some embodiments, a reaction space can be in a single-wafer ALD reactor or a batch ALD reactor where deposition on multiple substrates takes place at the same time. In some embodiments the substrate on which deposition is desired, such as a semiconductor workpiece, is loaded into a reactor. The reactor may be part of a cluster tool in which a variety of different processes in the formation of an integrated circuit are carried out. In some embodiments a flow-type reactor is utilized. In some embodiments a high-volume manufacturing-capable single wafer ALD reactor is used. In other embodiments a batch reactor comprising multiple substrates is used. For embodiments in which batch ALD reactors are used, the number of substrates is preferably in the range of 10 to 200, more preferably in the range of 50 to 150, and most preferably in the range of 100 to 130.

Examples of suitable reactors that may be used include commercially available ALD equipment such as the F-120® reactor, F-450 reactor, Pulsar® reactors—such as the Pulsar® 2000 and the Pulsar® 3000—EmerALD® reactor and Advance® 400 Series reactors, available from ASM America, Inc of Phoenix, Ariz. and ASM Europe B.V., Almere, Netherlands. Other commercially available reactors include those from ASM Japan K.K (Tokyo, Japan) under the tradename Eagle® XP and XP8. In addition to these ALD reactors, many other kinds of reactors capable of ALD growth of thin films, including CVD reactors equipped with appropriate equipment and means for pulsing the precursors can be employed. In some embodiments a flow type ALD reactor is used. Preferably, reactants are kept separate until reaching the reaction chamber, such that shared lines for the precursors are minimized. However, other arrangements are possible.

Suitable batch reactors include, but are not limited to, reactors designed specifically to enhance ALD processes, which are commercially available from and ASM Europe B.V (Almere, Netherlands) under the trade names ALDA400™ and A412™. In some embodiments a vertical batch reactor is utilized in which the boat rotates during processing, such as the A412™. Thus, in some embodiments the wafers rotate during processing. In some embodiments in which a batch reactor is used, wafer-to-wafer uniformity is less than 3% (1 sigma), less than 2%, less than 1% or even less than 0.5%.

The germanium oxide ALD processes described herein can optionally be carried out in a reactor or reaction space connected to a cluster tool. In a cluster tool, because each reaction space is dedicated to one type of process, the temperature of the reaction space in each module can be kept constant, which improves the throughput compared to a reactor in which the substrate is heated up to the process temperature before each run.

According to some embodiments, a germanium oxide thin film is formed by an ALD-type process comprising multiple pulsing cycles, each cycle comprising:

-   -   pulsing a vaporized first Ge precursor into the reaction chamber         to form at most a molecular monolayer of the Ge precursor on the         substrate,     -   removing excess Ge precursor and reaction by products, if any,     -   providing a pulse of a second oxygen reactant comprising an         oxygen source onto the substrate,     -   removing excess second reactant and any gaseous by-products         formed in the reaction between the Ge precursor layer on the         first surface of the substrate and the second reactant, and     -   repeating the pulsing and removing steps until a germanium oxide         thin film of the desired thickness has been formed.

In some embodiments germanium oxide, preferably GeO₂, is deposited from alternating and sequential pulses of a Ge precursor and an oxygen source, like water, ozone, oxygen plasma, oxygen radicals, or oxygen atoms. In some embodiments the oxygen source is not water. The Ge precursor preferably comprises Ge(OEt)₄ or TDMAGe.

The Ge precursor employed in the ALD type processes may be solid, liquid, or gaseous material under standard conditions (room temperature and atmospheric pressure), provided that the Ge precursor is in vapor phase before it is conducted into the reaction chamber and contacted with the substrate surface. “Pulsing” a vaporized precursor onto the substrate means that the precursor vapor is conducted into the chamber for a limited period of time. Typically, the pulsing time is from about 0.05 seconds to about 10 seconds. However, depending on the substrate type and its surface area, the pulsing time may be even higher than about 10 seconds.

Preferably, for a 300 mm wafer in a single wafer ALD reactor, the Ge precursor is pulsed for from about 0.05 seconds to about 10 seconds, more preferably for from about 0.1 seconds to about 5 seconds and most preferably for from about 0.3 seconds to about 3.0 seconds. The oxygen-containing precursor is preferably pulsed for from about 0.05 seconds to about 10 seconds, more preferably for from about 0.1 seconds to about 5 seconds, most preferably for from about 0.2 seconds to about 3.0 seconds. However, pulsing times can be on the order of minutes in some cases. The optimum pulsing time can be readily determined by the skilled artisan based on the particular circumstances.

As mentioned above, in some embodiments the Ge precursor is Ge(OEt)₄ or TDMAGe. Other possible germanium precursors that can be used in some embodiments are described below. In some embodiments, the Ge precursor is Ge(OMe)₄. In some embodiments the Ge-precursor is not a halide. In some embodiments the Ge-precursor may comprise a halogen in at least one ligand, but not in all ligands.

The oxygen source may be an oxygen-containing gas pulse and can be a mixture of oxygen and inactive gas, such as nitrogen or argon. In some embodiments the oxygen source may be a molecular oxygen-containing gas pulse. The preferred oxygen content of the oxygen-source gas is from about 10% to about 25%. Thus, one source of oxygen may be air. In some embodiments, the oxygen source is molecular oxygen. In some embodiments, the oxygen source comprises an activated or excited oxygen species. In some embodiments, the oxygen source comprises ozone. The oxygen source may be pure ozone or a mixture of ozone, molecular oxygen, and another gas, for example an inactive gas such as nitrogen or argon. Ozone can be produced by an ozone generator and it is most preferably introduced into the reaction space with the aid of an inert gas of some kind, such as nitrogen, or with the aid of oxygen. In some embodiments, ozone is provided at a concentration from about 5 vol-% to about 40 vol-%, and preferably from about 15 vol-% to about 25 vol-%. In other embodiments, the oxygen source is oxygen plasma.

In some embodiments, ozone or a mixture of ozone and another gas is pulsed into the reaction chamber. In other embodiments, ozone is formed inside the reactor, for example by conducting oxygen containing gas through an arc. In other embodiments, an oxygen containing plasma is formed in the reactor. In some embodiments, the plasma may be formed in situ on top of the substrate or in close proximity to the substrate. In other embodiments, the plasma is formed upstream of the reaction chamber in a remote plasma generator and plasma products are directed to the reaction chamber to contact the substrate. As will be appreciated by the skilled artisan, in the case of a remote plasma, the pathway to the substrate can be optimized to maximize electrically neutral species and minimize ion survival before reaching the substrate.

In some embodiments the oxygen source is an oxygen source other than water. Thus, in some embodiments water is not provided in any ALD cycle for depositing GeO₂.

In some embodiments the Ge precursor comprises at least one amine or alkylamine ligand, such as those presented in formulas (2) through (6) and (8) and (9), and the oxygen precursor comprises water.

Before starting the deposition of the film, the substrate is typically heated to a suitable growth temperature, as discussed above. The preferred deposition temperature may vary depending on a number of factors such as, and without limitation, the reactant precursors, the pressure, flow rate, the arrangement of the reactor, and the composition of the substrate including the nature of the material to be deposited on.

The processing time depends on the thickness of the layer to be produced and the growth rate of the film. In ALD, the growth rate of a thin film is determined as thickness increase per one cycle. One cycle consists of the pulsing and removing steps of the precursors and the duration of one cycle is typically between about 0.2 seconds and about 30 seconds, more preferably between about 1 second and about 10 seconds, but it can be on order of minutes or more in some cases, for example, where large surface areas and volumes are present.

In some embodiments the GeO₂ film formed is a pure GeO₂ film. Preferably, aside from minor impurities no other metal or semi-metal elements are present in the film. In some embodiments the film comprises less than 1-at % of metal or semi-metal other than Ge. In some embodiments the GeO₂ film is stoichiometric. In some embodiments, a pure GeO₂ film comprises less than about 5-at % of any impurity other than hydrogen, preferably less than about 3-at % of any impurity other than hydrogen, and more preferably less than about 1-at % of any impurity other than hydrogen.

In some embodiments, the GeO₂ film formed has step coverage of more than about 80%, more preferably more than about 90%, and most preferably more than about 95% in structures which have high aspect ratios. In some embodiments high aspect ratio structures have an aspect ratio that is more than about 3:1 when comparing the depth or height to the width of the feature. In some embodiments the structures have an aspect ratio of more than about 5:1, or even an aspect ratio of 10:1 or greater.

Ge Precursors

A number of different Ge precursors can be used in the ALD processes. In some embodiments the Ge precursor is tetravalent (i.e. Ge has an oxidation state of +IV). In some embodiments, the Ge precursor is not divalent (i.e., Ge has an oxidation state of +II). In some embodiments, the Ge precursor may comprise at least one alkoxide ligand. In some embodiments, the Ge precursor may comprise at least one amine or alkylamine ligand. In some embodiments the Ge precursor is a metal-organic or organometallic compound. In some embodiments the Ge precursor comprises at least one halide ligand. In some embodiments the Ge precursor does not comprise a halide ligand.

In some embodiments the Ge precursor is not solid at room temperature (e.g., about 20° C.).

For example, Ge precursors from formulas (1) through (9) below may be used in some embodiments. GeOR₄  (1)

Wherein R is can be independently selected from the group consisting of alkyl and substituted alkyl; GeR_(x)A_(4-x)  (2)

Wherein the x is an integer from 1 to 4;

R is an organic ligand and can be independently selected from the group consisting of alkoxides, alkylsilyls, alkyl, substituted alkyl, alkylamines; and

A can be independently selected from the group consisting of alkyl, substituted alkyl, alkoxides, alkylsilyls, alkyl, alkylamines, halide, and hydrogen. Ge(OR)_(x)A_(1-x)  (3)

Wherein the x is an integer from 1 to 4;

R can be independently selected from the group consisting of alkyl and substituted alkyl; and

A can be independently selected from the group consisting of alkyl, alkoxides, alkylsilyls, alkyl, substituted alkyl, alkylamines, halide, and hydrogen. Ge(NR^(I)R^(II))₄  (4)

Wherein R^(I) can be independently selected from the group consisting of hydrogen, alkyl and substituted alkyl; and

R^(II) can be independently selected from the group consisting of alkyl and substituted alkyl; Ge(NR^(I)R^(II))_(x)A_(1-x)  (5)

Wherein the x is an integer from 1 to 4;

R^(I) can be independently selected from the group consisting of hydrogen, alkyl and substituted alkyl; and

R^(II) can be independently selected from the group consisting of alkyl and substituted alkyl;

A can be independently selected from the group consisting of alkyl, alkoxides, alkylsilyls, alkyl, substituted alkyl, alkylamines, halide, and hydrogen. Ge_(n)(NR^(I)R^(II))_(2n+2)  (6)

Wherein the n is an integer from 1 to 3;

R^(I) can be independently selected from the group consisting of hydrogen, alkyl and substituted alkyl; and

R^(II) can be independently selected from the group consisting of alkyl and substituted alkyl; Ge_(n)(OR)_(2n+2)  (7)

Wherein the n is an integer from 1 to 3; and

Wherein R can be independently selected from the group consisting of alkyl and substituted alkyl; Ge_(n)R_(2n−2)  (8)

Wherein the n is an integer from 1 to 3; and

R is an organic ligand and can be independently selected from the group consisting of alkoxides, alkylsilyls, alkyl, substituted alkyl, alkylamines. A_(3-x)R_(x)Ge-GeR_(y)A_(3-y)  (9)

Wherein the x is an integer from 1 to 3;

y is an integer from 1 to 3;

R is an organic ligand and can be independently selected from the group consisting of alkoxides, alkylsilyls, alkyl, substituted alkyl, alkylamines; and

A can be independently selected from the group consisting of alkyl, alkoxides, alkylsilyls, alkyl, substituted alkyl, alkylamines, halide, and hydrogen.

Preferred options for R include, but are not limited to, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tertbutyl for all formulas, more preferred in ethyl and methyl. In some embodiments, the preferred options for R include, but are not limited to, C₃-C₁₀ alkyls, alkenyls, and alkynyls and substituted versions of those, more preferably C₃-C₆ alkyls, alkenyls, and alkenyls and substituted versions of those.

In some embodiments the Ge precursor comprises one or more halides. Preferably the precursor comprises 1, 2, or 3 halide ligands. However, as mentioned above, in some embodiments the Ge precursor used in the ALD process does not comprise a halide.

In some embodiments, a Ge precursor that comprises an alkoxide is not used in combination with water in an ALD process. In other embodiments, an amine/akylyamine or Ge-N bond containing Ge precursor may be used in combination with water. Preferred alkylamine Ge precursors include, but are not limited to, tetrakis(dimethylamino) germanium (TDMAGe), tetrakis(diethylamino) germanium (TDEAGe), and tetrakis(ethylmethylamino) germanium (TEMAGe). In some embodiments the Ge precursor is TDMAGe. In some embodiments the precursor is TDEAGe. In some embodiments the precursor is TEMAGe.

Examples

GeO₂ films were deposited in an F-450 ALCVD R&D reactor at temperatures ranging from about 150° C. to about 300° C. using germanium ethoxide (Ge(OEt)₄) or tetrakis(dimethylamino) germanium (TDMAGe) as the Ge precursor, and ozone (O3) as the oxygen source. Ge(OEt)₄ is a liquid with a vapor pressure of about 0.2 Torr at 55° C. TDMAGe is a liquid with a vapor pressure of about 3 Torr at 50° C. Pulse/purge times were 3.0 s/6.0 s for all precursors Ge(OEt)₄, TDMAGe and O₃. In these deposition experiments the Ge precursor was held at room temperature. The O₃ flow rate was 100 sccm. Film thicknesses were measured using a spectroscopic ellipsometer and x-ray diffraction XRR (Bruker AXS D8 Advance). Composition was determined by Rurherford backscattering spectroscopy RBS.

In one set of experiments, GeO₂ films were deposited by alternately and sequentially contacting a substrate in a reactor chamber with vapor pulses of Ge(OEt)₄ and O₃ at about 150° C. to about 300° C. In this temperature range growth rate of about 0.18 Å/cycle to about 0.3 Å/cycle was obtained (FIG. 1).

In the same temperature range of 150° C. to 300° C. the thickness non-uniformity was about 3% to about 13% 1-sigma, and the lowest non-uniformities were obtained at 300° C. (FIG. 3). A series of films of various thicknesses were deposited at 250° C. by varying cycle number. Film growth was linear, i.e. film thickness can be controlled by the number of cycles (FIG. 4). Thinner films were also deposited at 300° C. Between about 150° C. and about 300° C., the GeO₂ film density was about 3.8 g/cm³ to about 4 g/cm³ (from XRR; bulk 4.23 g/cm³). In particular, at 250° C. the growth rate was about 0.25 Å/cycle and the film had a non-uniformity of less than about 10%. The XRR density at 250° C. was about 4.35 g/cm³ (bulk 4.23 g/cm3), and the refractive index was modeled to be close to the bulk value from ellipsometer data (bulk 1.650 vs. modeled 1.66).

In the temperature range of 150° C. to 250° C., the composition of these films was about 32-at % Ge and about 68-at % O (RBS analysis of about 50 nm GeO₂ on silicon with native oxide). See FIG. 5.

Electrical results (capacitance-voltage i.e. C-V) of GeO₂ films deposited by ALD on Ge-substrates (both n- and p-type) using vapor pulses of Ge(OEt)₄ and O₃ can be seen in FIG. 11 through FIG. 14B. In some samples, GeO₂ ALD deposition was followed by Al₂O₃ ALD film deposition using TMA as aluminum source and ozone or water as oxygen source. It can be concluded from the electrical results that a GeO₂ interlayer deposited by ALD provides good electrical properties including low Dit (interfacial traps) and Dbt (border traps), as well as small CV hysteresis for capacitors on p-Ge. Promising performance can thus be expected for transistors. No electrical degradation was found when ALD-deposited GeO₂ interlayer thickness was reduced from about 5 nm to about 2.2 nm. It also can be concluded that the k value of ALD-deposited GeO₂ is about 5.7. An ALD-deposited Al₂O₃ capping layer is preferable in some situations. Native Ge oxide can also be removed prior to the GeO₂ ALD deposition. Better performance was also observed for ALD-deposited GeO₂ interlayers grown at 250° C. compared to 300° C.

In FIGS. 7A and 7B it can be seen that GeO₂ deposited by ALD grows linearly on HF-last Ge (FIG. 7B) and on HF-last Si (FIG. 7A) when using vapor pulses of Ge(OEt)₄ and O₃ at 300° C.

FIGS. 8A and 8B show TEM images of an ALD Al₂O₃/ALD GeO₂ (37 cycles)/Ge/Si-stack/structure. Al₂O₃ was deposited by ALD using vapor pulses or TMA and water or ozone. As can been seen from FIG. 8B, layers can mix when using water as an oxygen source in the Al₂O₃ ALD process, whereas when using ozone as the oxygen source in the Al₂O₃ ALD process, two clearly separated layers can be seen in FIG. 8A. However, the reason for intermixing of the layers is unsure, and it may be caused by the electron beam in the analysis.

Good conformality can be obtained when depositing GeO₂ by ALD using vapor pulses of Ge(OEt)₄ and O₃ as can be seen in FIGS. 9A and 9B and in FIG. 10, which illustrates ALD GeO₂/ALD HfO₂ stack film conformality when grown at a reaction temperature of 250° C. and using a target GeO₂ thickness of about 30 nm.

In another set of experiments, GeO₂ films were deposited by alternately and sequentially contacting a substrate in a reactor chamber with vapor pulses of tetrakis(dimethylamino)germanium (TDMAGe) and O₃ at 150° C. to 300° C. In this temperature range growth rate of about 0.4 Å/cycle to about 0.55 Å/cycle was obtained. In the same temperature range of 150° C. to 300° C., the thickness non-uniformity was less than about 6%. The best nonuniformity of less than about 2% was observed at about 200° C. In the 150° C. to 300° C. range, the GeO₂ film density was about 3.8 g/cm³ to about 4 g/cm³ (from XRR). The EDX composition was about 30 at. % Ge and about 70 at. % O. TDMAGe was also observed to react with water.

GeO₂ was also deposited on a Ge surface and topped with HfO₂. Briefly, 50 nm of GeO₂ was deposited from TDMAGe and O₃ by ALD, as described herein, on a substrate comprising either 15 nm or 1 μm Ge on Si. Subsequently, approximately 50 nm of HfO₂ was deposited over the GeO₂ by atomic layer deposition using alternating and sequential pulses of HfCl₄ and H₂O. The deposition temperature was 300° C. No etching was observed. The results are shown in FIGS. 6A and 6B.

Although certain embodiments and examples have been discussed, it will be understood by those skilled in the art that the scope of the claims extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses and obvious modifications and equivalents thereof. 

What is claimed is:
 1. A deposition process for forming a thin film comprising germanium oxide and less than 5-at % of metal other than germanium on a substrate by multiple sequential deposition cycles, each of the sequential deposition cycles comprising: contacting the substrate with a vapor phase tetravalent germanium precursor comprising at least one ligand selected from alkyl, alkoxide, amine, and alkylamine, such that a molecular monolayer comprising germanium is formed on the substrate surface, contacting the substrate with a vapor phase oxygen precursor, wherein the oxygen precursor reacts with the monolayer comprising germanium on the substrate surface.
 2. The process of claim 1, each of the multiple deposition cycles further comprising removing excess germanium precursor and reaction byproducts, if any, from the substrate surface prior to contacting the substrate with the vapor phase oxygen precursor.
 3. The process of claim 1, each of the multiple deposition cycles further comprising removing excess oxygen precursor and reaction byproducts, if any, from the substrate surface prior to beginning a subsequent deposition cycle.
 4. The process of claim 1, wherein the multiple sequential deposition cycles include only a germanium precursor and an oxygen precursor.
 5. The process of claim 1, wherein the oxygen precursor comprises ozone, oxygen atoms, oxygen radicals, or oxygen plasma.
 6. The process of claim 1, wherein the germanium precursor comprises an alkylamine ligand and the oxygen precursor comprises water.
 7. The process of claim 6, wherein the germanium precursor has a formula Ge_(n)(NR^(I)R^(II))_(2n+2) and R^(I) and R^(II) can be independently selected from methyl and ethyl.
 8. The process of claim 6, wherein the germanium precursor has a formula Ge_(n)(NR^(I)R^(II))_(2n+2) and R^(I) and R^(II) can be independently selected from C₃, C₄, C₅, and C₆ alkyls.
 9. The process of claim 1, wherein the surface of the substrate comprises germanium oxide prior to beginning the deposition process.
 10. The process of claim 1, wherein the substrate is pretreated before the thin film is formed.
 11. The process of claim 10, wherein the pretreatment comprises exposing the substrate to a passivation chemical.
 12. The process of claim 10, wherein the pretreatment comprises forming an interfacial layer on the substrate surface.
 13. The process of claim 10, wherein the pretreatment comprises removing native Ge oxide from the substrate surface.
 14. The process of claim 1, further comprising depositing a layer comprising a different material over the thin film.
 15. The process of claim 14, wherein the different material comprises a high-k material.
 16. The process of claim 1, wherein the thin film is used in a Ge-condensation process.
 17. An atomic layer deposition (ALD) process for forming a thin film comprising germanium oxide and less than 5-at % of metal other than germanium, the process comprising at least two sequential deposition cycles, each of the at least two sequential deposition cycles comprising: alternately and sequentially contacting a substrate with a germanium precursor comprising at least one alkyl, alkoxide, amine, or alkylamine ligand and an oxygen source, wherein the germanium precursor is not divalent.
 18. The process of claim 17, wherein the germanium precursor comprises Ge(OCH₂CH₃)₄ and the oxygen source comprises O₃.
 19. The process of claim 17, wherein the germanium precursor comprises TDMAGe, and the oxygen source comprises ozone.
 20. The process of claim 17, wherein the germanium precursor comprise TDMAGe, and the oxygen source comprises water. 